Looks like Stlakid is right, I will try a set. Here is a reply from NGK:
Hello,
The CR9EK plug is a dual ground electrode design. The Iridium IX plug
that will most closely match this plug is a single ground electrode plug
CR9EIX stock no. 3521. Thank you.
Kristopher Zdral
Technical Support Representative
NGK Spark Plugs (U.S.A.), INC.